From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 85440108E1FE for ; Thu, 19 Mar 2026 12:22:30 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AD6B16B049E; Thu, 19 Mar 2026 08:22:29 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A87856B04A0; Thu, 19 Mar 2026 08:22:29 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9CB206B04A1; Thu, 19 Mar 2026 08:22:29 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 8C5C86B049E for ; Thu, 19 Mar 2026 08:22:29 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 1B3081604E9 for ; Thu, 19 Mar 2026 12:22:29 +0000 (UTC) X-FDA: 84562725618.05.F88B94D Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf26.hostedemail.com (Postfix) with ESMTP id 4D77714000A for ; Thu, 19 Mar 2026 12:22:27 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf26.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1773922947; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NoDUHnsqcrd3qtBz0MzbtUQ4Qt0DSZv3jE11sc/V9Hc=; b=e5HnoRwmAxxkEbwO57M1W/tQ6WbXVm18J78MY/woglFzDVClraJw95t+rWPg6kyIbWzUWz 3yevNLdikr23vS6xqI8bQ7lYoYL76WWtiObOX51H53u9ZNkqQathzeXp/JhOmyeF7aVB9o yMSSgAcEUY0MsuZjtIadg9uEzl5ZG0k= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf26.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773922947; a=rsa-sha256; cv=none; b=1vrcRnL6eZM6eYos6XhmYSTX1yF1RVKRIME/h4fjH0ul7h3nSRz0elcdmvJyBL+CaEYIQ4 r8lHgwYm+dZw2R9b3pqwxkD6z863yA96xKZQN+W1xpQVQ8V04AFosRrhrTemh/yWtTY/wT DKJKfREjsp6yqCCY8PFRVgew+wlZzQo= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 513311A25; Thu, 19 Mar 2026 05:22:20 -0700 (PDT) Received: from [10.57.85.34] (unknown [10.57.85.34]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A6B7C3F778; Thu, 19 Mar 2026 05:22:21 -0700 (PDT) Message-ID: <0d963ff9-9222-4e0f-8e57-ff22088ce978@arm.com> Date: Thu, 19 Mar 2026 12:22:19 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/3] vmalloc: add __GFP_SKIP_KASAN support Content-Language: en-GB To: Muhammad Usama Anjum , Arnd Bergmann , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Kees Cook , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Konovalov , Marco Elver , Vincenzo Frascino , Peter Collingbourne , Catalin Marinas , Will Deacon , david.hildenbrand@arm.com References: <20260319114952.3241359-1-usama.anjum@arm.com> <20260319114952.3241359-2-usama.anjum@arm.com> From: Ryan Roberts In-Reply-To: <20260319114952.3241359-2-usama.anjum@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4D77714000A X-Stat-Signature: paa7xj7o9fokdzth461xux1nnd4xkpnz X-Rspam-User: X-HE-Tag: 1773922947-966932 X-HE-Meta: U2FsdGVkX18womOphIEy+X8XvjPYsrYMarg4G0/YisCfLv7gh+AwxxyVGNpoIHtpTov5EYqcs2nm94ESoyjBla0oj6/0Vp/qwgIz0ZanZ8q3S4vsG08uxt2D4gu32iAzHGnFGSgjMVGq4TKmYO8iN7EbxiSf5eVeK72FahTno+LI4KD4k9kYDT8Wek+f/yOa3WUdR4exDEkGqM4+E5Fg9JBOCa8mzBjR5nUA+bcavmqukFbAM346APlHjoyKsUKkcZJ2EWPC+97H3XCQBy6msdqi4y1mAPspWKz2B4Izyk3xRCTEQumeBtP6NhujvnvcdRBs3T9Pb1P9xQrWVpSiS+KKNXsKXI63BiV4GZR95MOZ4qi2Vg9WH8aBa1BkkfmcE+S8kCbYqO+cdf8x4RyqAarj0KylsTmWEKXUmuzNi9wF8aUFx++fhRnJIcpy67d/mcTC6xiYvyTjzuRD0RvmvWnAPzf0QkK2EhD0SFKaDylpvZSXUX4fv0uaf/Ef3hS4AioL7tWIXQvAdoVUXvQAwSPQcoEgQjjwhM/9jatlS00emlFZE3cp5lKRYgolT88bEGB+y74wqZXYpZbbDOFxL1plwLZ2Uro+6To8h2R5u+afNleJV4p5cJ6ChWwy+YbV0vvLIPTNJ/X05WZQGflkYOos7rb7Ai5FbnwCTWzeEqtCSJm2IR5Bqq/EDDZLvciGtmMKQjYBL0TomfUtiNgySAwYCxt14FUxIaWmXMa6Vkn9NzgnHJ+jI+9sC775aLn0CrHpPhGyyz4bFLt/QQIIj+h06AFqSqBIc10AV/i5mszN/ZkTfCdQ1w1ahgbPArw6omC6zb0gp1oF44B1fqBSKecHg1GakE2+ovSdhrB0JvFisVDD2fUSgOzEOu4OQPRVMb68/9j1ZnAVWizOu0PbCsEINxJtezBETiU8rqCd0s2IZ6xbF8WH5C2GoWouLfg9/ooxu8ktzrGcDeWqcjl OiqgIexm 9IJ6+sAgAoP+2KVv2VveoZDEEs9ZB+5lsnQqvcmUB6c21Pp2E0RmMA4D+IIjh17KCmF9TMuaz1vjadC0w8BL8/xHYdNPs31owbjX3CxgJ4f6C3md/B6DE3WvoqAUK7gKcZHomhEpVQLVTtPgsWPCPsOe5jEhZhBdoPSVWcUvJYqZHwiJ0GYfgGcALkLqnBGdZ2QLFtHaNirMTeSXqpUMJD2tLULGhGuBZd+Gwq+FZXaCsT0Y= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 19/03/2026 11:49, Muhammad Usama Anjum wrote: > For allocations that will be accessed only with match-all pointers > (e.g., kernel stacks), setting tags is wasted work. If the caller > already set __GFP_SKIP_KASAN, don’t skip zeroing the pages and > don’t set KASAN_VMALLOC_PROT_NORMAL so kasan_unpoison_vmalloc() > returns early without tagging. > > Before this patch, __GFP_SKIP_KASAN wasn't being used with vmalloc > APIs. So it wasn't being checked. Now its being checked and acted > upon. Other KASAN modes are unchanged because __GFP_SKIP_KASAN isn't > defined there. > > This is a preparatory patch for optimizing kernel stack allocations. > > Signed-off-by: Muhammad Usama Anjum > --- > mm/vmalloc.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index c607307c657a6..1baa602a0b9bb 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -4041,7 +4041,10 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align, > * kasan_unpoison_vmalloc(). > */ > if (pgprot_val(prot) == pgprot_val(PAGE_KERNEL)) { > - if (kasan_hw_tags_enabled()) { > + bool skip_kasan = kasan_hw_tags_enabled() && > + (gfp_mask & __GFP_SKIP_KASAN); > + > + if (kasan_hw_tags_enabled() && !skip_kasan) { It's unfortunate that kasan_hw_tags_enabled() is involved twice in this expression. > /* > * Modify protection bits to allow tagging. > * This must be done before mapping. > @@ -4057,7 +4060,8 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align, > } > > /* Take note that the mapping is PAGE_KERNEL. */ > - kasan_flags |= KASAN_VMALLOC_PROT_NORMAL; > + if (!skip_kasan) > + kasan_flags |= KASAN_VMALLOC_PROT_NORMAL; I wonder if it would be clearer to just not call kasan_unpoison_vmalloc() below if the user passed in __GFP_SKIP_KASAN? It's really just an implementation detail that kasan_unpoison_vmalloc() skips unpoisoning if KASAN_VMALLOC_PROT_NORMAL is not provided. Thanks, Ryan > } > > /* Allocate physical pages and map them into vmalloc space. */